In the fabrication of semiconductor wafers several process steps require contacting the wafers with fluids. Examples of such process steps include etching, photoresist stripping, and prediffusion cleaning. The chemicals utilized in these steps often comprises strong acids, alkalis, or solvents. The equipment conventionally used for contacting semiconductor wafers with process fluid consists of a series of tanks or sinks into which boats of semiconductor wafers are dipped.
Removing the wafers from the tank often results in contamination, which is detrimental to the microscopic circuits which the fabrication process creates. Since the chemicals generally are manufactured by chemical companies and shipped to the semiconductor manufacturing plant, the initial chemical purity is limited by the quality of the water used by the chemical manufacturers, the container used for shipping and storing the chemical and the handling of the chemical. Additionally, the etching bath is contaminated from the build-up of impurities both dissolved and undissolved in the process bath during the processing of the semiconductor wafers. Moreover, as chemicals age, they can become contaminated with impurities from the air and from the wafers.
Thus, the etching solution must be changed periodically. The treatment of the last batch of wafers prior to fluid rejuvenation may not be as effective as treatment of the first batch of wafers in a new solution. Non-uniform treatment is a major concern in semiconductor manufacturing.
In semiconductor processing involving wet etching and cleaning, bath contamination at the air/liquid interface of the bath surface cannot be completely removed by air or liquid filtration. Therefore, when semiconductor wafers are removed from a wet etching/cleaning bath, the wafers become contaminated by the contaminants present at the air/liquid interface of the bath.
The present invention overcomes the drawbacks of the prior etching/cleaning methods by reducing the surface contaminants in a wet etching bath. The present invention provides a method for rapidly removing a substantial portion of the etching liquid from the bath such that the contaminants are removed from the air/liquid interface of the bath.